206 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



part of the shaft is in typical later andesite. On the 400-foot level the andesite 

 is of somewhat different character, being greenish and altered, but its characters 

 still indicate that it is probably the later andesite. On this level it contains some 

 calcite veinlets, but no quartz. On the 500-foot level the andesite is finer grained 

 than on the 400, and has some of the features of the earlier andesite, but there 

 is little doubt that it belongs to the same body as the 400-foot level, and the 

 balance of evidence is therefore in favor of considering it probably later andesite. 

 On this level there are some calcite stringers and some narrow quartz veinlets, 

 containing, however, practically no values. At a depth of 550 feet in the shaft 

 a change of formation was reported, and the material seen on the dump taken 

 from beneath this point is largely a dense, green, siliceous rock containing quartz 

 stringers. A specimen of this examined microscopically proved to be of the 

 glassy Tonopah rhyolite-dacite. Inspection of the dump indicates that this 

 rhyolite-dacite is mixed with some andesite, which may be either the earlier or 

 the later andesite, so far as microscopic characteristics go. 



The above data indicate that at this point the later andesite is considerably 

 thicker than in the territory farther east. Indeed, its lower limit is uncertain. 



